Novel, sulfide-resistant antistatic yarn

ABSTRACT

Silver coated nylon yarn can be rendered sulfide resistant without destruction of static dissipation characteristics or basic fiber characteristics by coating the yarn with particular alloys of two or more samples of the group comprising bismuth, lead, tin and cadmium.

United States Patent Weiner Feb. 19, 1974 [54] NOVEL, SULFIDE-RESISTANT ANTISTATIC 1,856,475 5/1932 Frost 1 17/114 BU YARN 2,515,022 7 1950 Snyder et a1. 117/114 B 3,203,826 8/1965 Stobierski 117/114 B X Inventor: Robert Weiner, fluntmgdon 1,907,890 5/1933 Steckel 117 114 B Valley, Pa. [73] Assignee: Rohm and Haas Company, FOREIGN PATENTS OR APPLICATIONS Philadelphia, Pa. 576,875 4/1946 Great Britain 204/21 297,161 91928 G tB 't' 29 195 E 122 Filed: Nov. 3, 1971 I m am [21] Appl 195483 Primary Examiner-A. B. Curtis [52] 11.8. C1. 29/19l.6, 29/195 P, 29/199, 1 17/ l 14 B 57 ABSTRA T [51] Int. Cl B32b 15/00 1 C [58] held of Search 75/134 166 166 D; Silver coated nylon yarn can be rendered sulfide resis- 29/195 195 1916 199; 117/114 82; tant without destruction of static dissipation charac- 204/21 43 teristics or basic fiber characteristics by coating the yarn with particular alloys of two or more samples of [56] References C'ted the group comprising bismuth, lead, tin and cadmium.

UNITED STATES PATENTS 7/1967 Dytrt 29/195 P 6 Claims, N0 Drawings 1 NOVEL, SULFlDE-RESISTANT ANTISTATIC YARN This invention relates to a novel anti-static yarn, to a method of manufacturing such yarn and to products produced from the yarn.

Many attempts have been made to provide an antistatic yarn, i.e., a yarn with a reduced tendency to accumulate static charge. These include the use of treating agents for the yarns, the introduction of additives into the basic fiber-forming component of the yarn, the inclusion of metal wiring or filaments in the yarn bundles, and the coating of fibers and filaments with metals. The modification of the basic fiber-forming composition and the treating of the yarn with various agents provide only limited improvement; the antistatic characteristics can be significantly humidity-dependent, and they may interfere with the dye-ability or increase the soil affinity of the fiber. Further, the treating agent often is lost during the first year of yarn usage.

The use of metallic wires in yarns (e.g., in carpet usage) presents a number of serious problems. The metal wire can be extremely difficult to camouflage and significantly affects the appearance of the yarn. The physical properties of the metal wire differ very significantly from the other filaments of the yarn as do the wear characteristics and the hand of the yarn. The presence of wire in a carpet, especially if plied, can cause significant streaking patterns in the carpet upon soiling or wearing as well as upon dyeing. The metal filaments, upon wearing, tend to break, presenting the problem of metal slivers in the carpet. The metal wires are so highly conductive that a shock hazard is presented should the carpet come in contact with house current, e.g., through defective wiring. Since metallic filaments cannot readily be textured in the same manner that, e.g., a nylon filament can be textured, it is customary to ply metallic filaments with the carpet yarn. This produces a yarn having buried and exposed metallic fibers;

the buried metallic yarn is essentially ineffective for static control and the exposed metallic yarn is easily damaged by normal traffic.

Ultimately it was found that nylon fiber substrates could be provided with a conductive metal coating to provide a product having good electrical conductivity and thus ready dissipation of static. In particular it has been found that the coating of nylon substrates with a silver coating can be effected in a manner to provide an exceptional antistatic yarn product on which the silver coating is quite durable and adherent. This coating can be attained without significant alteration of the basic mechanical characteristics of the nylon substrate, an advantage not generally available by other processes or by the use of other metals. The product contains a built-in safeguard against shock from defective household wiring since the heat from high current loads would melt the nylon core thereby causing collapse of the conductive path.

In the utilization of such fibers, however, it is common for yarn bundles to be bonded together and back coated with a foamed latex backing. When the latex backing contains sulfur curing agents and when the latex backing is cured at elevated temperature, serious degradation of the silver coating can result. Apparently this results from reaction of the sulfur in a manner that interrupts the conductive path such that the fiber loses its anti-static character. The sulfur contamination normally present under ordinary use conditions of the car peting does not create this problem with the silver coated nylon substrates. The problem appears clearly to be related to the elevated temperature used in curing operations and the types of curing agents used.

Latex-backed carpeting represents a very substantial portion of the field of use for nylon carpet yarns. Unfortunately the problem of sulfur degradation is not easily resolved. A number of agents have been applied to protect the silver coating from the sulfide contamination but these altered the basic characteristic of the silver coated yarn. For example, some treatments while preventing sulfide contamination, interfered with the conductive character of the yarns. Other treatments thought to be useful actually dissolved or removed the silver coating from the yarn. Still other techniques, while providing some degree of protection, effectively destroyed the basic mechanical characteristics of the yarn and it was no longer characterized by the nylon filamentary substrate.

It has now been found that many of the foregoing problems can be overcome by applying to a silver coated nylon substrate a molten alloy of specific composition and characteristics. More specifically the alloys useful for the purposes of the present invention are those alloys of two or more metals of the group consisting of bismuth, lead, tin and cadmium, which have a melting point in the range of about C. up to about C. and in which no individual metal is present in an amount greater than 60 percent. The following are examples of alloys useful for the purposes of this invention.

ln the table above, some of the alloys are eutectic alloys exhibiting precise melting points. Others are noneutectic alloys exhibiting a melting range. Unless otherwise specified, for the purposes of this disclosure and the claims, the term melting point as applied to noneutectic alloys is that temperature at which all of the components of the alloy are in the molten state.

The silver-coated nylon is coated with a molten alloy by hot dipping processes. Typically, the silver-coated nylon can be passed through a bath of the molten alloy maintained at a temperature at least 5 above the melting point of the base alloy. In selecting the specific alloy, care must be exercised to consider the substrate being treated. For example, if the temperature of the bath were to exceed C, the tenacity of the nylon substrate would decrease and the physical characteristics of the product would be unsuitable for general textile usage. If the melting point of the alloy is too low, the subsequent handling of carpeting or other materials made from the yarn will tend to remove or destroy the protective coating. For example, an effective coating can be applied to a silvered nylon substrate using molten Wood's alloy (50 percent bismuth, 24 percent lead, 14 percent tin, 12 percent cadmium). This alloy has a melting point of 71C. The bath of Woods alloy, held at 80 90C., can readily be used for hot dipping of nylon substrates to provide a good coating. However, when the resulting product is incorporated into a carpeting and the carpeting passed through a dye bath maintained at about 100C., the Woods alloy again tends to melt; the agitation and physical handling of the carpet in the dye bath tends to cause the molten Woods alloy to bead up and/or be removed from the silvered substrate. Such alloys are unsuitable for the purposes of the present invention. Similarly, the temperatures and treatments encountered in a curing oven when a latex is applied to the back of carpeting must be taken into account in selecting the alloy. In general, however, while the oven temperatures often are of the order of 150C., the type of treatment encountered in the oven is comparatively gentle and the likelihood of destruction of the coating is less likely. It is however preferred that the alloy used have a melting point of at least 140C. to ensure against possible losses of the coating during subsequent carpet treatments.

The preferred system is based on tin, lead and cadmium. While bismuth-containing alloys are useful and can provide an excellent sulfide resistant coating, the handling of molten bismuth presents possible safety hazards. The presence of bismuth vapor over the molten alloy is a health hazard and can be avoided most easily by using a bismuth-free alloy. Accordingly, the invention will be described hereinafter with respect to the preferred alloy system which comprises 50 percent tin, 32 percent lead, and 18 percent cadmium. This alloy has a melting point of about 145C. This should not however be construed as a limitation on the invention, since other of the alloys described previously are also operable and useful.

The procedure used to obtain the silver coating on the nylon substrate is not critical to the success of the present invention provided a firmly adherent coating is obtained. The procedures described subsequently represents one way in which this may be accomplished.

Fifteen denier, nylon 6 yarnis knit into a continuous nylon sleeve on a Textile Machine Works C-B-Tex Machine with a 400 needle knitting heat at 48 courses per inch. The sleeve is not heat set. The sleeve is then scoured for thirty minutes in thirty parts by weight of a scouring liquor per part by weight of nylon; the liquor contains percent each of t-octylphenoxypoly (9) ethoxyethanol and tetrasodium pyrophosphate based on the weight of fiber. The sleeve is then rinsed in cold water until all evidence of sudsing disappears, and is air dried. The scoured and dried sleeve is sensitized with, for example, a solution of anhydrous stannic chloride in denatured ethyl alcohol (1 gram of salt per 10 ml. of solution). The sleeve is soaked for five minutes in the sensitizing solution, washed and then passed into a silvering bath prepared by adding, in sequence, to 6300 ml. of water, 1.58 grams of sodium lauryl sulfate, 625 ml. of 0.30N silver nitrate solution, 612 m1. of 1N ammonium hydroxide, 160 ml. of 1N acetic acid (to bring the silvering bath pH to 9.0) and 371 ml. of 2.4 percent formaldehyde solution. The sleeve is retained in the bath for 165 minutes with occasional stirring and then removed from the bath, rinsed with water to remove the silvering solution, and dried.

The dried sleeve, metallized to 14 percent silver coating based on the weight of fiber, is again scoured in the manner described, following which it is boiled in water for two hours. The metallized sleeve after drying is deknit on a cone winder at about 400 yards per minute to give 9 cones of silver plated fiber. It is customary to treat a knit sleeve with a lubricating agent for the deknitting operation. When the silvered substrate is to be further metal coated, the lubricant selected for the deknitting operation should desirably be a water soluble lubricant. This water-soluble lubricant can be easily removed after deknitting in an aqueous bath such as a mixture of water and isopropanol in volume proportions of 9 to 1. The cleaned, silvered fiber is then dried and is ready for coating in accordance with the teachings of the present invention.

It is not critical for the coating operation that the fiber be held under tension. As a practical matter, however, it is generally useful to pass the fiber through a tension gate wherein moderate tension, e.g., 2 grams, is maintained. The fiber is then passed into the molten metal bath which is maintained at a fairly constant temperature in the range of about 155 175C. It is to be noted that this temperature range was selected for use with the preferred alloy of this invention which has a melting point of about C. A different temperature might be more suitable with lower or higher melting alloys. In a typical operation the fiber path through the molten metal is about 10 15 cm. long. The fiber leaves the molten bath over an exit guide containing a slight groove. The groove wipes the excess metal off the fiber forming a molten bead which hangs on the guide over the fiber and acts as an exit jet, thereby providing a relatively smooth and uniform coating. Typically the exit guide may be formed from polytetrofloroethylene (Teflon), or other suitable materials such as aluminum. If excessive solids in the form of metal oxides form in the bath and accumulate in the bead, there is a tendency for the bead to solidify with concommitant breakage of the fiber. This solids formation can be at least partially controlled by covering the bath with a nitrogen atmosphere. However it appears a slight amount of oxide is necessary to form a satisfactory bead.

The coating solidifies on the fiber as it leaves the bath. The coated fiber is collected on the tubes at from about 50 yards/minute. Subsequently the fibers can be lubricated and re-wound into more suitable packages. The electrical resistivity of the coated fiber is about 20 70 ohms per 1- /2 inch length. This is approximately 1 10th the resistivity of the silvered nylon, giving the product more than sufficient conductivity to be an effective dissipator of static electricity. However, as with the silvered nylon, the product has a built-in safeguard with respect to large current flows which will melt the nylon substrates.

Pieces of ordinary carpet yarn were wrapped with the coated fibers produced in the manner described above. The composite yarns are placed on a watch glass and covered with a piece of cheese-cloth. A commercial sulfur-curing latex is then applied to the cheese cloth and the entire mass is cured in an oven at 300F for 15 minutes. The coated fibers are removed from the carpet yarn and are tested to determine how effective a leakage path the filaments provide for a high voltage source (variable from O 15,000 volts). The coated fibers produced in accordance with the present invention provide a leakage path that allowed a voltage build-up of less than volts. A similarly treated silver coated fiber of the type which was used in the process of the present invention was so badly degraded by the sulfur that there was virtually no leakage path and voltage build-up of about 15,000 volts was encountered.

In another method of effecting the coating of the silvered nylon substrate, the fiber was passed through a molten metal bath for approximately 3 cm. of immersion, following which the fiber was withdrawn through a plate floating on the metal surface. The plate used in this test consisted merely of a polytetrofloroethylene plate with a hole made by a 25 gauge needle. The fiber passed from the bath up through the hole as nearly vertically as reasonably possible to the next guide. It was found that this type of a guide permitted easy, rapid and uniform coating of the fiber without regard for the need of a bead. When the run was conducted at about 150C. of metal temperature, a slight problem was encountered due to metal solidifying at the top of the hole in the plate. Thus the metal temperature should generally be in excess of 5 above its melting point to minimize the dangers of undesirable solidification and breakage of the fiber. Typically, speeds on the order of 315 ft./minute were found reasonable with this type of plate.

For commercial production a molten metal bath is suitably prepared, using a generally rectangular stainless steel trough approximately 6 inches long, 2 inches wide and 2 inches high. One of the end pieces of the trough is provided with a slot approximately 6 mils in width, having a rounded edge and rounded bottom. The slot extends to within about a quarter inch of the bottom of the trough. When the trough contains the molten metal at a temperature within the range of about 150 175C, surface tension prevents the alloy from draining from the slot. The fiber is then passed through the slot and enters the bath subsurfacely. Floating on the surface of the metal is an aluminum wiping guide through which the fiber passes as it leaves the bath. Typically thw wiping guide is 1- /2 inches l- /z inches and A; inch thick. The plate is provided with a capillary opening approximately mils in diameter. The capillary hole is countersunk 1/16 inch to leave a capillary land of approximately 1/16 inch. This wiping guide may conveniently be made in two sections in order to facilitate the lacing up procedure at start-up or in the event of yarn breakage.

It has been found that the fiber entering the bath tends to draw oxygen into the bath with it, leading to oxidation of the molten metal and a subsequent buildup of solids. To avoid this difficulty it has been found convenient to enclose the yarn in an appropriate purge chamber to which nitrogen is caused to flow immediately prior to the entry of the fiber into the molten metal bath. Following this procedure it has been found possible to produce the coated fibers product of the present invention at typical rates of 600 ft./minute.

In general it has been found desirable to follow the bath treatment by a curing and/or annealing heat treatment 5 to 10 below the melting point of the alloy coating. If this composition is not a eutectic alloy, then the temperature should be 5 to 10 below the melting point of the lowest melting component of the alloy composition.

In addition to the method described above, the present invention can be utilized to coat nylon fibers which have a polymeric coating in which silver particles are dispersed. Such yarns are described, for example, in US. Pat. No. 3,582,448. In this instance of course the alloy coating will only be bonded at points along the yarn which are exposed at the surface. However, a reasonably adherent alloy coating can be obtained by this means. It will be recognized however that the preferred embodiment utilizes a yarn having a generally continuous silver coating thereon.

Significantly, the fibers of the present invention do not present the electrical injury potential found when continuous metallic wires are used in carpets. In the event of contact with defective wiring, the nylon substrate will melt thereby causing collapse of the fiber and its conductive path, in the vicinity of the defective wiring. This, of course, breaks the circuit and the danger of serious electrical injury is minimized or eliminated.

What is claimed is:

1. An antistatic fiber comprising a nylon fiber substrate having a first coating of silver and a second coating of an alloy of at least two metals selected from the group consisting of bismuth, lead, tin and cadmium, said alloy containing not more than 60 percent by weight of any one of said selected metals, said alloy further characterized by a melting point in the range of C. up to C.

2. A fiber in accordance with claim 1 wherein said alloy is a ternary alloy of tin, lead and cadmium.

3. A fiber in accordance with claim 2 wherein said alloy is of essentially eutectic proportions.

4. A carpet having distributed therein the antistatic fibers of claim 1.

5. A method for rendering a silver-coated nylon fiber substrate resistant to sulfide corrosion comprising providing a melt of an alloy having a melting point in the range of 100C. to 175C. and made up of at least two metals of the group consisting of bismuth, lead, tin and cadmium; maintaining said melt at a temperature at least 5 above its melting point but not above C; passing said silver-coated nylon fiber substrate through said melt; passing said fiber through a guide adapted to distribute molten alloy adhering to said substrate evenly along said substrate to form a coating thereon; and solidifying said coating on said substrate.

6. A method in accordance with claim 5 wherein said coating is annealed at an elevated temperature below the melting point of said alloy. 

2. A fiber in accordance with claim 1 wherein said alloy is a ternary alloy of tin, lead and cadmium.
 3. A fiber in accordance with claim 2 wherein said alloy is of essentially eutectic proportions.
 4. A carpet having distributed therein the antistatic fibers of claim
 1. 5. A method for rendering a silver-coated nylon fiber substrate resistant to sulfide corrosion comprising providing a melt of an alloy having a melting point in the range of 100*C. to 175*C. and made up of at least two metals of the group consisting of bismuth, lead, tin and cadmium; maintaining said melt at a temperature at least 5* above its melting point but not above 180*C; passing said silver-coated nylon fiber substrate through said melt; passing said fiber through a guide adapted to distribute molten alloy adhering to said substrate evenly along said substrate to form a coating thereon; and solidifying said coating on said substrate.
 6. A method in accordance with claim 5 wherein said coating is annealed at an elevated temperature below the melting point of said alloy. 